FIG. 22 is a block diagram showing a structure of a conventional multi-channel input system. FIG. 22 shows a structure of a conventional multi-channel input system having a plurality of terminals and a radio keyboard corresponding to each terminal. The terminal and its corresponding keyboard are connected to each other via radio links according to a multi-channel system.
Specifically, the multi-channel input system is constructed of n terminals 101 to 10n, and n radio keyboards 201 to 20n that are connected to the terminals respectively. The terminals and radio keyboards transmit and receive key data by utilizing channels CH1 to CHn respectively.
The terminal 101 is a personal computer, which is connected to the radio keyboard 201 via a radio link. This terminal 101 is provided with a channel-setting switch 111 and a radio interface 121 in addition to a CPU (Central Processing Unit) and a memory not shown.
The channel-setting switch 111 is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn that can be utilized in the multi-channel input system to the radio interface 121. In the example shown in this drawing, the channel CH1 has been set to the radio interface 121 by the channel-setting switch 111.
The radio interface 121 is an interface for receiving the key data from the radio keyboard 201 via the radio link by utilizing the channel CH1 set by the channel-setting switch 111.
The radio keyboard 201 is connected to the terminal 101 via the radio link. This radio keyboard 201 is provided with a key section 211, a channel-setting switch 221, and a radio interface 231.
The key section 211 is constructed of alphabet keys, number keys, function keys, a space key, and an enter key. Each time when each key is depressed, a key code corresponding to this key is output.
The channel-setting switch 221 is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn (the same channel as that set to the radio interface 121) to the radio interface 231. In the example shown in this drawing, the channel CH1 has been set to the radio interface 231 by the channel-setting switch 221.
The radio interface 231 is an interface for transmitting the key data from the key section 211 via the radio link by utilizing the channel CH1 set by the channel-setting switch 221.
The terminal 102 is a personal computer, which is connected to the radio keyboard 202 via a radio link. This terminal 102 is provided with a channel-setting switch 112 and a radio interface 122 in addition to a CPU and a memory not shown.
The channel-setting switch 112 is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn that can be utilized in the multi-channel input system to the radio interface 122. In the example shown in this drawing, the channel CH2 has been set to the radio interface 122 by the channel-setting switch 112.
The radio interface 122 is an interface for receiving the key data from the radio keyboard 202 via the radio link by utilizing the channel CH2 set by the channel-setting switch 112.
The radio keyboard 202 is connected to the terminal 102 via the radio link. This radio keyboard 202 is provided with a key section 212, a channel-setting switch 222, and a radio interface 232.
The key section 212 is constructed of alphabet keys, number keys, function keys, a space key, and an enter key. Each time when each key is depressed, a key code corresponding to this key is output.
The channel-setting switch 222 is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn (the same channel as that set to the radio interface 122) to the radio interface 232. In the example shown in this drawing, the channel CH2 has been set to the radio interface 232 by the channel-setting switch 222.
The radio interface 232 is an interface for transmitting the key data from the key section 212 via the radio link by utilizing the channel CH2 set by the channel-setting switch 222.
Similarly, the terminal 10n is a personal computer, which is connected to the radio keyboard 20n via a radio link. This terminal 10n is provided with a channel-setting switch 11n and a radio interface 12n in addition to a CPU and a memory not shown.
The channel-setting switch 11n is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn that can be utilized in the multi-channel input system to the radio interface 12n. In the example shown in this drawing, the channel CHn has been set to the radio interface 12n by the channel-setting switch 11n. 
The radio interface 12n is an interface for receiving the key data from the radio keyboard 20n via the radio link by utilizing the channel CHn set by the channel-setting switch 11n. 
The radio keyboard 20n is connected to the terminal 10n via the radio link. This radio keyboard 20n is provided with a key section 21n, a channel-setting switch 22n, and a radio interface 23n. 
The key section 21n is constructed of alphabet keys, number keys, function keys, a space key, and an enter key. Each time when each key is depressed, a key code corresponding to this key is output.
The channel-setting switch 22n is a DIP switch or a dial switch, and this is a manual switch for setting one of the channels CH1 to CHn (the same channel as that set to the radio interface 12n) to the radio interface 23n. In the example shown in this drawing, the channel CHn has been set to the radio interface 23n by the channel-setting switch 22n. 
The radio interface 23n is an interface for transmitting the key data from the key section 21n via the radio link by utilizing the channel CHn set by the channel-setting switch 22n. 
In the above structure, for setting the channel CH1 to the terminal 101 and the radio keyboard 201 corresponding to this terminal respectively, a user operates the channel-setting switch 111 to set the channel CH1 to the radio interface 121, and then operates the channel-setting switch 221 to set the channel CH1 to the radio interface 231.
Similarly, for setting the channel CH2 to the terminal 102 and the radio keyboard 202 corresponding to this terminal respectively, other user operates the channel-setting switch 112 to set the channel CH2 to the radio interface 122, and then operates the channel-setting switch 222 to set the channel CH2 to the radio interface 232.
According to the above-described conventional multi-channel input system, there is no mechanism for managing the channel setting in the system as a whole. Therefore, users cannot easily understand channels that have been set at other terminals and radio keyboards.
For the above reason, there occurs such a situation that the user of the terminal 102, for example, unconsciously sets the channel CH1 to the terminal 102 and the radio keyboard 202 without knowing that this channel CH1 has already been set at the terminal 101 and the radio keyboard 201.
In this case, there has been a problem that the terminal 101 can receive key data from both the radio keyboard 201 and the radio keyboard 202, and this results in the occurrence of interference.
Further, when the terminal 101 and the radio keyboard 202 are installed close to each other, the terminal 101 can receive the key data of the channel CH2 that has already been set to the other radio keyboard 202, in addition to the key data of the channel CH1 that has been set to the own terminal.
Further, there has been a problem that even if the set channel of the terminal 101 and the radio keyboard 201 has been changed from the channel CH1 to the channel CH2, the terminal 101 can receive the key data from both the radio keyboard 201 and the radio keyboard 202, and this results in the occurrence of interference.
Further, according to the conventional multi-channel input system, it is necessary to manually operate the channel setting switch after visually confirming the setting of other channels based on the status of other channel-setting switches. As a result, there has been a problem that it takes time to set the channels, and errors easily occur in the channel setting.